Problem: Solve for $x$ : $x^2 - 6x + 9 = 0$
Explanation: The coefficient on the $x$ term is $-6$ and the constant term is $9$ , so we need to find two numbers that add up to $-6$ and multiply to $9$ The number $-3$ used twice satisfies both conditions: $ {-3} + {-3} = {-6} $ $ {-3} \times {-3} = {9} $ So $(x {-3})^2 = 0$ $x - 3 = 0$ Thus, $x = 3$ is the solution.